1. Field of the Invention
The present invention relates to a signal processing apparatus which incorporates a signal processing circuit for processing weak signals susceptible to noises.
2. Description of the Related Art
Generally, a facsimile machine is well known as a machine incorporating a signal processing apparatus for processing relatively weak signals. Here, weak signals may include image signals at a reading section of the facsimile machine and aural signal at a calling section of the same machine.
The facsimile machine also includes optical sensing components for detecting image carrying paper sheets and recording paper sheets. Such an optical sensor may include a light emitting element such as an LED, and a light receiving element such as a phototransistor.
In the conventional facsimile machine, the LED as a light emitting element is periodically turned on and off by a pulse current for example. This is because if the LED is kept on for continuous light emission, it will lose its initial light-emitting performance, whereby the sensitivity of the optical sensor will be disadvantageously deteriorated. Further, if the LED is kept turned on, the life span of the LED will be unfavorably shortened.
However, when the LED is periodically turned on and off in the conventional manner described above, there is a problem of generating unfavorable noises in weak signal processing circuits due to the pulse currents. Those noises will unduly affect the weak signals, whereby the weak signal processing is not properly performed.
It is, therefore, an object of the present invention is to provide a signal processing apparatus for properly processing weak signal, such as image signals, without being affected by noises generated due to a pulse current.
According to one aspect of the present invention, there is provided a signal processing apparatus including a signal processing circuit for processing a weak signal susceptible to noises; an electronic component which is selectively energized and de-energized; a start/end determiner for determining initiation and termination of the weak signal processing; a conduction holder for causing the electronic component to be continuously energized when the start/end determiner determines the initiation of the weak signal processing; and a state changer for causing the electronic component to be intermittently energized when the start/end determiner determines the termination of the weak signal processing.
With such an arrangement, when the weak signal is processed, the electronic component is continuously energized, thereby generating no noise to affect the weak signal processing.
According to a preferred embodiment, the electronic component may include an optical sensor.
The weak signal may be or an image signal for example.
The conduction holder may cause the electronic component to be continuously energized by a steady current. On the other hand, the state changer may cause the electronic component to be intermittently energized by a pulse current.
According to a preferred embodiment, the start/end determiner, the conduction holder and the state changer may be provided by a central processing unit of a machine which incorporates the signal processing apparatus.
According to a preferred embodiment, the machine may be a facsimile machine.
According to another aspect of the present invention, there is provided a signal processing apparatus including a signal processing circuit for processing a weak signal susceptible to noises, an electronic component which is selectively energized and de-energized; and a controller for controlling the operation of the electronic component. The controller determines initiation and termination of the weak signal processing. The controller further causes the electronic component to be continuously energized upon determination of the initiation of the weak signal processing. The controller further causes the electronic component to be intermittently energized upon determination of the termination of the weak signal processing.
Other objects, features and advantages of the present invention will be apparent from the detailed description of the embodiment given below with reference to the accompanying drawings.